Effect of K+ and Cl? ion gradients upon apex regeneration in Acetabularia mediterranea

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Abstract
Regeneration of a new apex and electrical activity by anucleate posterior stalk segments (PSS) of Acetabularia mediterranea under imposed transcellular concentration gradients of K+ and Cl- has been studied. In a 3 vs. 30 mM K+ and in a 26 vs. 545 mM Cl- gradient, respectively, the PSS preferably regenerate at that end exposed to the low K+ (replaced by Na+) and low Cl- (replaced by SO 4 2- ), respectively. The effect of the K+ gradient confirms previous work where voltage-clamped PSS regenerated at the electrically hyperpolarized end (Novák and Bentrup, Planta 108, 227, 1972). The stimulation of regeneration by low Cl-, that is, at the depolarized end of the PSS, might be mediated by the electrical impulses arising at this end.